1. Field of the Invention
The present invention relates generally to valve devices that may be used in the construction of oil and gas wells. More specifically, the present invention relates to an improved pressure and differential-fill (PDF) valve used to position and cement casing into a wellbore.
2. Setting of the Invention
Differential-fill float and cementing assemblies employ a flow regulation valve in the casing string to permit forward circulation through the casing string and to automatically control the filling of the casing string with drilling fluid as the casing string is lowered into a well. Admitting regulated amounts of drilling fluid into the casing as it is being lowered into the wellbore reduces the suspended weight of the casing string, allows the casing to sink through the drilling fluid, prevents the casing from collapsing and reduces hydraulic ram forces against the subsurface formation. Once the casing is lowered into the proper position in the wellbore, a cement slurry is pumped through the casing string and cementing assembly into the annulus between the casing and the borehole. During this cementing process, the valving in the cementing assembly is remotely reconfigured to form a backpressure (check) valve for the purpose of preventing back-flow of the cement slurry pumped into the annulus. A complete description of differential-fill float and cementing equipment of the type with which the present invention may be employed may be found in U.S. Pat. No. 4,729,432 (herein, the xe2x80x9c""432 patentxe2x80x9d). The ""432 patent, belonging to the Assignee of the present application, is incorporated herein for all purposes.
The differential-fill operation of the assembly described in the ""432 patent is provided by a differential pressure valve comprised of a small, pivoting flapper valve xe2x80x9cpiggybackedxe2x80x9d on the flapper gate of a larger flapper check valve. The differential pressure valve and the flapper check valve cooperate to prevent back-flow of drilling fluid from the well into the casing until the differential pressure valve opens. The small flapper valve opens to permit a regulated amount of well fluid to flow into the casing through a flow passage in the gate of the check valve. A controlled strength spring constructed of hard spring-steel biases the small flapper valve to its closed position preventing back-flow of drilling fluid into the casing. When the differential pressure between the drilling fluid in the wellbore and that in the casing is sufficiently great, the spring bias is overcome and the small flapper valve pivots open to admit drilling fluid into the casing. The flapper spring closes the small flapper valve automatically when fluid admitted into the casing reduces the pressure differential below that required to open the valve. The flapper spring imposes a great deal of stress on the flapper hinge pin, requiring usage of a relatively large, high strength steel pin as the hinge pin.
After the casing has been cemented into the well, the differential-fill and cementing assembly must be milled or drilled out of the casing string. This removal process is facilitated by constructing the assembly with materials that are easily milled or cut by the drill bit. Brass and aluminum are commonly employed in the construction of the major structural components of the differential-fill and cementing equipment.
The springs used to regulate the opening of the regulating valves used in the differential-fill portions of the assembly are often provided by heavy coiled springs constructed of relatively hard spring-steel. The high strength steel flapper hinge pins and the steel springs, such as the pins and springs used for the small flapper valve of the ""432 patent, are very difficult for a polycrystalline diamond compact (PDC) bit to mill or drill out of the casing.
A feature of the assembly of the present invention is that a differential pressure poppet valve is centrally located in the differential-fill equipment and is moved along its central axis, parallel to the direction of fluid back-flow, as it travels between opened and closed positions. The poppet valve of the assembly operates without pivoting into and out of the centerline area of the flow stream and eliminates the need for a heavy steel hinge pin as is required for the flapper closure member of the prior art. The axial movement of the poppet valve maintains symmetrical flow past the valve to improve fluid flow regulation and minimize erosion of the valve components, which is particularly important where the components are constructed of plastics and/or composite materials. As compared with a standard piggybacked flapper arrangement, the configuration of the poppet valve and its placement on the flapper gate of the differential pressure valve of the present invention contribute to an increase in the flow passage dimensions through the differential-fill equipment when the flapper gate is fully opened.
When the invention is employed as a differential-fill valve for lowering casing into drilling fluid, the major structural components and the pressure regulating biasing spring of the differential-fill valve may be constructed of plastics and/or composite materials to facilitate the milling or drilling up of the valve. A leaf spring constructed of composite material may be employed to impose the biasing closing force on a poppet valve mounted in the flapper gate of the differential pressure valve. Elimination of a flapper valve as a regulating component of the differential-fill valve eliminates the need for a heavy steel hinge pin. In a preferred embodiment, the poppet valve, poppet valve biasing element, flapper valve and flapper hinge pin may be constructed of composite materials and/or plastics.
The regulating poppet valve feature of the present invention may be used in a combination, differential-fill and cementing assembly that is first used to automatically fill the casing as the casing is lowered into a wellbore and then is remotely reconfigured from the well surface to conduct a cement slurry from the casing into the annulus between the casing and the wellbore. The differential pressure valve also functions to provide a backpressure check valve to prevent back-flow of the cement slurry into the casing once the cement slurry has been pumped into the annulus. The major structural components of the assembly, including the pressure regulating spring of the differential fill valve, may be constructed of composite materials and/or plastics to facilitate the milling or drilling up of the assembly after the casing has been cemented into the wellbore.
As used herein, the term xe2x80x9ccomposite materialsxe2x80x9d is intended to mean a combination of two or more materials (reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macro scale. Constituents of composite materials retain their identities; that is, they do not dissolve or merge completely into one another although they act in concert. Normally, the components of composite materials can be physically identified and exhibit an interface between one another.
From the foregoing, it will be appreciated that a major objective of the present invention is to provide a poppet valve in the closure element of a differential pressure valve that permits improved regulation of a back-flow of fluid through the valve while minimizing turbulent fluid flow and valve erosion through the poppet valve.
An object of the present invention is to provide a subsurface fluid flow regulating valve in which the regulating portions of the valve are smoothly contoured and symmetrically oriented about a central axis and are moved in a direction parallel to the regulated fluid flow to improve flow regulation, minimize fluid turbulence and minimize erosion of the valve components.
A related object of the present invention is to provide a biasing spring constructed of a composite material that is sufficiently strong to bias the closure member of a regulating valve against the opening force of a pressurized fluid to maintain a predetermined pressure differential between the pressurized fluid and the area regulated by the valve.
Another important object of the present invention is to provide a regulating valve that can be easily drilled out of a casing string by a PDC bit.
Yet another object of the present invention is to provide a combination differential-fill and cementing valve assembly constructed primarily of plastics and/or composite materials whereby the assembly may be easily drilled out of a casing string with a PDC bit. A related object of the invention is to eliminate the need for a heavy steel flapper hinge pin in the regulating portions of the cementing valve assembly.
The foregoing objects, features and advantages of the present invention, as well as others, will be more fully appreciated and better understood by reference to the following drawings, specification and claims.